Biomedical subjects

Simon Benhamou

Publications and source records attributed to Simon Benhamou.

5 recordsLinked to original sources

PubMed2006

What do European badgers (Meles meles) know about the spatial organisation of neighbouring groups?

European badgers (Meles meles) live in groups. Although they can distinguish between a member of their own group, a member of a neighbouring group and a stranger, their ability to understand that neighbouring individuals belong to different groups inhabiting different places, and possibly to build up some representation of the spatial organisation of neighbouring groups remains to be shown. In this study, we conducted a pilot homing experiment to test such ability. Radio-collared badgers were displaced to the home ranges of neighbouring groups and their homing performances were compared to those of badgers displaced either to the periphery of their own group's home range or beyond the neighbouring home ranges. When released in their own home range, badgers homed rapidly and efficiently, whereas when released beyond the neighbouring groups' home ranges (whatever the distance) they did not home. In contrast, badgers released in the home range of a neighbouring group performed some random search there, before returning to their setts quite efficiently. These results suggest that badgers may consider their neighbours as members of different groups inhabiting different places close to their own home range, but their ability to build up some spatial representation of neighbourhood relationships could not be demonstrated.

Animals↗

PubMed2006

Detecting an orientation component in animal paths when the preferred direction is individual-dependent.

An orientation component leads to directionally biased paths, with major consequences in animal population redistribution. Classical orientation analyses, which focus on the overall direction of motion, are useless for detecting such a component when the preferred direction is not common to the whole population, but differs from one path to another. In-depth path analyses are required in this case. They consist of determining whether paths are more suitably represented as biased or unbiased random walks. The answer is not easy because most animals' paths show some forward persistence propensity that acts as a purely local directional bias and, hence, blurs the possible occurrence of an additional, consistent bias in a preferred direction. I highlight the key differences between biased and unbiased random walks and the different ways orientation mechanisms can generate a consistent directional bias. I then examine the strength and weakness of the available methods likely to detect it. Finally, I introduce a new procedure based on the backward evolution of the beeline distance, from the end of the path, which might correspond to a goal toward which the animal orients itself, to each of the animal's preceding locations. This new procedure proves to be very efficient, as it requires only a small sample of short paths for detecting a possible orientation component.

Animal Migration↗

PubMed2004

How to reliably estimate the tortuosity of an animal's path: straightness, sinuosity, or fractal dimension?

The tortuosity of an animal's path is a key parameter in orientation and searching behaviours. The tortuosity of an oriented path is inversely related to the efficiency of the orientation mechanism involved, the best mechanism being assumed to allow the animal to reach its goal along a straight line movement. The tortuosity of a random search path controls the local searching intensity, allowing the animal to adjust its search effort to the local profitability of the environment. This paper shows that (1) the efficiency of an oriented path can be reliably estimated by a straightness index computed as the ratio between the distance from the starting point to the goal and the path length travelled to reach the goal, but such a simple index, ranging between 0 and 1, cannot be applied to random search paths; (2) the tortuosity of a random search path, ranging between straight line movement and Brownian motion, can be reliably estimated by a sinuosity index which combines the mean cosine of changes of direction with the mean step length; and (3) in the current state of the art, the fractal analysis of animals' paths, which may appear as an alternative and promising way to measure the tortuosity of a random search path as a fractal dimension ranging between 1 (straight line movement) and 2 (Brownian motion), is only liable to generate artifactual results. This paper also provides some help for distinguishing between oriented and random search paths, and depicts a general, comprehensive framework for analysing individual animals' paths in a two-dimensional space.

Animals↗

PubMed2003

Bicoordinate navigation based on non-orthogonal gradient fields.

The mathematically exact solution for navigating with respect to two non-orthogonal gradient fields requires taking both fields into account conjointly. Such a complex solution may be beyond the brain capability of most animals. Animals may use an approximate, simpler solution by considering each field separately (i.e., the angle between the two gradient directions is ignored). This generates directional biases that may prove useful in determining the nature of the fields actually involved in bicoordinate navigation.

Animals↗

PubMed2003

Homing in pelagic birds: a pilot experiment with white-chinned petrels released in the open sea.

During the breeding period white-chinned petrels (Procellaria aequinoctialis) repeatedly perform long foraging trips in the open ocean from their breeding island, and are able to home with an astonishing precision. The orientation mechanisms involved are not yet known. By analogy with those used by desert ants moving in a similarly "featureless" environment, one can hypothesise that petrels may home using path-integration. We displaced 11 white-chinned petrels 725-785km from their burrows to the open sea, preventing them from using visual and magnetic route-based information. Three birds carried satellite transmitters. Our results showed that they can home rather efficiently in such conditions.

Journal Article↗